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Example: The half-cell reaction: 2Fe2+ + 3H2O = Fe2O3(s) + 6H+ + 2e

This half-cell reaction can be decomposed into three simpler reactions, only two of which are found in Table 10.1:

A^ o(Fe/Fe2+) = -2x96.5x0.44 = -85 kJ/mole A^(Fe/Fe2O3) = -120x4.184 = 502 kJ/mole A^o(H2O/O2) = -4x96.5 x(-1.23) = 475 kJ/mole

The first and last of these half-cell reactions are numbers 7 and 1, respectively, in Table 10.1. The middle reaction does not involve either aqueous ions or electrons; its free energy change (at 25oC) is obtained from the Ellingham diagram of Fig. 10.3. The free energy change of the desired half-cell reaction is obtained by algebraically combining the above three component reactions:

A^°(Fe2+/Fe2O3) = 3/2 A^°(H2O/O2) + 3/2 A^°(Fe/Fe2O3) - 2 A^°(Fe/Fe2+) = 129 kJ/mole Converting this to the half-cell EMF by use of Eq (10.30) yields:

Problem 10.2 is another example of combining entries in Table 10.1 to obtain the standard electrode potential of a reaction not listed in the table.

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Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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